Yokogawa 2-Wire Dual Channel Transmitter/Analyzer FLXA21 Manual do Utilizador descarregar pdf (Página 59)

<4. COMMISSIONING OF pH/ORP>

4-5

IM 12A01A02-01E 5th Edition : Oct. 31, 2013-00

l Matrix

Matrixmeansatemperaturecompensationwhichusesthetemperaturecompensation

matrix.ThetemperaturecompensationmatrixisatableofpHvaluesatvarioustemperatures

correspondingtothepHvaluesatthestandardtemperature.Fordetails,seeAppendix1.

When the temperature or the precompensated pH value is out of the range of the temperature

compensationmatrix,thetemperaturecompensationerror(warning)willbeissued.Thisisnota

device error.

Inthiscase,however,thetemperaturecompensationisperformedbyextrapolation.

NOTE

TodisplaytheprecompensatedpHvalue,settheProcessTemp.Compensationto“None”.

SelectMeasurementsetup→Temp.compensation→ProcessTemp.Compensation.

l NEN6411

This algorithm takes into account the dissociation of water in strong acid and strong alkaline

solutions. It is particularly useful for pH measurement of boiler feed water.

4.2.4 Calibration settings

Thescreenowdiffersdependingonthecombinationofobjectstobemeasured.

Calibration settings for a pH converter involve slope (sensitivity), zero (aspot), and ITP

(isothermalpoint).Figure4.2showsthepHvalueagainstthemVoutputofthesensor.The

characteristicforpHmeasurementisanoffsetalsoknownasaspot[mV]orzero[pH]anda

Slope[%,mV/pH].Foranidealsensor,thetheoreticalslopeis59.16mV/pHat25ºC.Theslope

canbeenteredinmV/pHorasapercentageofthetheoreticalslope(100%correspondsto

59.16mV/pH).ITPrepresentsapHvaluewheretheoutputofthesensordoesnotchangewith

temperature.Notethatslopeandzeroaredenedat25ºC.

ΔpH

ΔmV

ITP (Isothermal point)

Aspot

0 mV

0 °C

10 °C

25 °C

500

- 200

ITP Zero

Figure 4.2 Calibration parameters

pH settings

l Zero and Slope units

Zero is an alternative to Asymmetry Potential. The method of zero (aspot) unit conforms to the

DINstandardforIEC60746-2instruments.ZeroisdenedinpHormV.

TheunitofSlope(sensitivity)ismV/pHor%(withthetheoreticalvalueas100%).

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